This invention relates to a programmable controller (PLC) device comprised of a main body which is formed by connecting a CPU unit with one or more I/O units through a bus line and a source unit for supplying power to the main body.
FIG. 14 is a block diagram showing the structure of a conventional PLC as a whole, including a main body unit 50a, a first expansion unit 50b-1, power units 1A, a CPU unit 2, I/O units 3, special function (SF) units 4, a bus connector 6 provided to the main body unit for external connection, bus connectors 7 and 8 provided to the first expansion unit for external connection and parallel bus lines PB. Briefly described, this PLC system is formed by connecting a single main body unit 50a and one or more expansion units 50b-1-50b-n through connector bus lines PB′.
The main body unit 50a includes a PLC main body formed by connecting a CPU unit 2, one or more I/O units 3 and a special function unit 4 through a parallel bus line PB and a power unit 1A for supplying power to this PLC main body. The first expansion unit 50b-1 includes an inner unit array formed by connecting one or more I/O units 3 and a special function unit 4 through a parallel bus line PB and a power unit 1A for supplying power to this unit array.
Such a PLC system is also referred to as being of a so-called building block type, and the structure with a parallel bus line PB provided on a back plane and the structure having partitioned parallel bus lines PB which are directly connected and each provided to one of the individual units have been known. In other words, PLC devices of the type comprised of a PLC main body formed with a CPU unit 2, one or more I/O units 3 and a special function unit 4 connected through a parallel bus line PB and a power unit 1A for supplying power to the PLC main body has conventionally been known.
Since the power unit 1A contained in the main unit 50a or the first expansion unit 50b-1 is for supplying power to the PLC main body in the main unit 50a or the unit array in the first expansion unit 50b-1, if it fails, the main unit 50a and the first expansion unit 50b-1 become incapacitated and there may be a serious consequence on the controlled target object. Since power units of this type contain a component with a finite useful lifetime such as an electrolytic capacitor, failures due to secular degradation are inevitable.
In view of above, Japanese Patent Publication Tokkai 2003-243269 disclosed an electric power source device for supplying power to an electronic apparatus adapted to measure the temperature of the electrolytic capacitor contained within the power source device, to estimate the lifetime of the device based on the result of a measurement and to display the result of the estimate on a 7-segment display device attached to the outer surface of the power source device or to provide an external output contact point for switching when the lifetime becomes less than a specified value.
As shown in FIG. 14, however, conventional PLC devices do not have a data transmitting path for exchanging data between the PLC main body inclusive of the I/O units 3 and the special function unit 4 and the power unit 1A. Thus, even if the function for estimating the lifetime is incorporated in the power unit 1A, the lifetime data obtainable therefrom cannot be utilized by the PLC main body unless a special external wiring is provided.
Thus, if the lifetime data obtainable from the power unit 1A could be taken to a specified area within a memory of the CPU unit 2 (accessible by a command word forming the user program or the system program), various meaningful applications would become possible by using such data in the user program or the system program.